Aspects of the present invention are directed to a method of controlling non-process of record (POR) process limiting yield (PLY) inspection work.
In wafer processing technologies, a set of wafers on which integrated circuits are to be imprinted are built in accordance with scheduled wafer starts, which establishes a number of wafers that are to be built. In this regime, a number of those wafers will need to be inspected for defects and/or other abnormalities to identify issues that may negatively impact the total wafer yield and the economic benefit of the wafer set. Typically, the number of the wafers to be inspected is established by process limiting yield (PLY) capacity planning.
Scheduled wafer starts are wafers that are started or built for the purpose of being inspected and is referred to as process of record (POR) work for inspection tools. Additional loading on the inspection tools is engineering work referred to as non-POR and has no associated wafer start schedule. That is, such work lies outside of the PLY planning capacity.
Capacity planning is indeed often unable to account for this additional loading since such planning may, in fact, not be possible due to the possibility of inspection schedules changing dynamically and event driven work. For example, with respect to a given wafer start schedule, an issue may arise that relates to an unknown issue in existence at the time of the capacity planning and may require inspection tool access that could not have been anticipated, planned for or scheduled. Unfortunately, current systems have little or no ability to track current dynamic available capacity and often only limit POR work sent to PLY inspection tools causing all of the work to build up at the tool in an unconstrained manner. Thus, since work at the PLY tools can build up in the unconstrained manner, the backlog may cause high Xfactor issues, inspection delays that can cause tool inhibits and missed/delayed critical inspection data.